Some radio communication devices communicate in more than one licensed frequency band. For example, a mobile cellular telephone may communicate more than one of the following bands US-GSM (824–894 MHz), E-GSM (880–960 MHz), PCN1800 (1710–1880 MHz), PCS1900 (1850–1990 MHz).
One RF antenna arrangement 10 that enables a radio communication device to communicate in the multiple bands is illustrated in FIG. 1.
The antenna arrangement 10 comprises: a feed point 12; a ground (short-circuit) point 14 connected to a ground plane 16; a first planar antenna element 21 extends between the feed point 12 and the ground point 14 to form a first loop antenna 31 of electrical length L1′; and a second planar antenna element 22 extends between the feed point 12 and the ground point 14 to form a second loop antenna 32 of electrical length L2′.
The ground plane 16 may be a printed wiring board (PWB). In this example it is rectangular having a width W and a length L. The ground plane 16 is parallel to the first and second planar elements 21, 22 but is displaced from them so that the first and second planar elements 21, 22 lie in a plane that is separated from the ground plane 16 by a distance H.
To save space the second planar antenna element 22 lies inside the area circumscribed by the first planar antenna 21. That is the first loop antenna 31 surrounds the second loop antenna 32. This is particularly useful when the antenna arrangement 10 is used internally in a hand-portable radio communication device, such as a mobile cellular telephone.
The first loop antenna 31 has a lowest resonant mode at a frequency corresponding to λ/2=L1′ and a second lowest resonant mode at a frequency corresponding to λ=L1′. The second loop antenna 32 has a lowest resonant mode at a frequency corresponding to λ/2=L2′.
The bandwidth of the lowest resonant mode of the first loop antenna 31 may be tuned by varying L and H. The lowest resonant mode of the first loop antenna 31 may be used either for one of the US-GSM and E-GSM bands or, if the bandwidth is tuned to a large value, by optimizing L and H, for both the US-GSM and E-GSM bands. The second lowest resonant mode of the first loop antenna 31 is used for the PCN1800 band or the PCS1900 band. The lowest resonant mode of the second loop antenna 32 is used for the other one of the PCN1800 band and the PCS1900 band.
Although the described antenna arrangement has a number of advantages such as its multi-band operation and reasonably compact design, it would be desirable to provide an alternative multi-band antenna arrangement, preferably with a more compact design.